Brief Description: RH Lower Flange Countersinks and Nutplates
My backing plate idea worked beautifully! I settled on using a 1.25 x 1.25 x 1/8 thick aluminum angle and matching drilling into the nutplate rivet holes. Then I took a drill the same size as the screw hole (it wasn't full size - you do that when you do the CS and knife edge the hole) and made a drill start mark on the angle using the screw hole as a guide. This centered what will become the pilot hole in the screw hole and drilled a #30 hole for the pilot.
Using my slow electric drill I drilled the countersinks to the proper size for #8 screw holes. This setup seemed to work better than using my air drill. The secret is to go full speed and press hard. I didn't have any chatter if I did that, and my countersinks were all chatter-free and smooth. I repeated with same process with the #6 screw holes for the access panels for a #40 pilot. One nice thing about the backing plate is the back side of the screw holes had no burrs that needed to be cleaned up.
Instead of priming, I used Q-tips and Bonderite. I found the best way to evenly apply the Bonderite on the CS surface was to stick the soaked Q-tip into the hole for two minutes. This kept the liquid in contact with the surface for even coverage. Rinsed throughly with water and dried.
I finished out the session by installing all of the nutplates on the screw holes. The only thing left is to countersink and apply Bonderite to the remaining rivet holes.
Backing plate in place. CSinks are good now with the proper size pilot guiding the cutter
Max CS diameter for #8 holes is 0.370 in. This is close enough.
I treated the bare CS surface with Bonderite. The Q-tips keep the liquid in contact with the surface.
